6.5 weeks - cannot see definitive sac *WORRIED*

So, after going to a&e last night and having blood tests and seeing gynocologist .. Who said my womb was closed and had a scan today, the man said that he couldn't confirm the definitive sac as it kept changing shape! Oval - to oblong.

My hormone levels are 2657 and he wants me to come back into the hospital tomorrow for more blood tests and needs the level to double in order to confirm a new scan date!

Has anyone had this? And had successful pregnancy, he said it may just still be early but I thought at that many weeks you should be able to see and I am very worried first time baby!

My HCG was particularly low and no detail pole see at first scan, I worried...pointlessly as 28weeks now with a healthy pregnancy. Try and keep positive (easier said than done I know - I hated people saying it to us). If it's meant to be, it will be. Fingers crossed for you both x